ARE will use a digester (~1 ton capacity) and anaerobic microbes (Bacteroides sp.or Clostridium sp.) to convert solid residues (small fibers < 1 mm) to biogas and a nutrient rich liquid. The process conditions (approximately 10-15% total solids; 5-20 days fermentation at 25-30 °C) and other important process parameters such as pH and C:N ratio are statistically optimized at bench scale level. Followed by digestion, the undigested solids are filtered using a screw press.
Typical digester gas is composed of 60-65% methane, 30-35% CO2, and 3% H2S. This gas mixture is treated with water in an absorber to remove CO2 and H2S, and the upgraded gas contains 98% methane per unit volume of gas (biogas to vehicle fuel standards). The biogas is collected and used for heating purposes; for example, bioethanol distillation or drying of mulch or fertilizer products.
Compositional analysis includes: (a) Nutrient, ash, carbohydrate, and lignin contents of the digester feed and output residue will be determined by standard analytical procedures; and (b) Similarly, the digester gas composition (hydrocarbon, carbon dioxide, hydrogen sulfide, nitrogen, and oxygen) and physical properties (heating value and density) are measured by gas chromatograph / mass spectrometer (GC / MS).
